This invention relates to hole openers for horizontal directional drilling. In particular, this invention relates to the attachment of cone arms to the bit body of hole openers.
During the installation of pipes, conduits, or other types of lines, it may be necessary to provide a horizontal pathway through areas that are not easily excavated. Such areas may include preexisting structures, environmentally sensitive areas, areas in which there is high traffic flow, and the like.
One method used to create a pathway without excavation is horizontal directional drilling. In horizontal directional drilling, a pilot hole is drilled along the pathway. After the pilot hole is drilled, a hole opener is pulled and/or pushed back through the pilot hole to enlarge the diameter of the hole to the desired size.
Typically, the hole opener includes a bit body with pockets to hold cone arms that perform the cutting action. Each of the cone arms include an arm secured into a corresponding pocket and further includes a cone head having the teeth formed thereon that cut the hole. Gaps between the pockets provide space for the rearward exit of debris.
Under the extreme stress of the drilling operation, cone arms can fracture from the bit body. In the event of such failure, the hole opener must be repaired. At a minimum, the repair requires replacement of the failed cone arm. However, in many cases, a wall of the pocket may fracture and this wall will need to be rebuilt. Thus, any cone arm failure or “break out” can be costly as the cone arm may need to be discarded or, if possible, repaired. This may result in substantial downtime, upsetting the construction schedule.
Hence, a need exists for an improved hole opener that is less prone to cone arm break out and pocket fracture.